The invention relates to a plug to seal the openings which are provided to accommodate anode rods in anode blocks, wherein the anode blocks are designed especially for the electrolytic extraction of base metals, such as aluminum, during their calcination treatment.
Base metals such as aluminum, magnesium and alkaline-earth metals are extracted by electrolysis from molten salts which contain the respective metals as cations. The technical production occurs in an electrolytic cell with a pan to hold the melt into which anodes, held by anode rods, are immersed. The anode rods are inserted into recesses of the anode blocks and sealed with molten iron. Lifting devices grip the anode rods to lower the anodes into the molten salt and to raise the spent anode blocks. The anode blocks themselves either consist of coal or a mixture of coke granules and pitch, which is compacted in a form tool and pressed into blocks. During the pressing process the recesses, possibly provided with pulls, are created for the later insertion of the anode rods. The anode blocks, which at this stage of the operation are also called green anodes, are subsequently moved through a cooling track, where they are cooled with water to increase their solidity. Subsequently, the anodes are subjected to calcination in a calcining furnace. To this end the upright anodes are consolidated into bundles--of six, for instance--and positioned by a crane or similar device on the bottom of the furnace. The calcining furnaces are invariably designed to accommodate several such bundles of anode blocks; in one case, for instance, having the capacity to hold a total of 90 anode blocks wherein the upright anodes are appropriately arranged in three rows, one above the other. Calcination should occur in an atmosphere as free of oxygen as possible. For this reason, before the furnace is sealed by a cover, the remaining gaps between the anode blocks are closed with a fill material consisting of coke granules. It has also been tried already to close the openings for the anode rods with plugs before inserting the anode blocks into the furnace. The plugs of the prior art are made of the same material as that of the anode blocks. For the calcining of the anode blocks the furnace is heated to over 800.degree. C. and the treatment lasts about 25 to 30 days. During the calcination process the fill material is unavoidably baked onto, conglutinated and even fused with the anode material. Because of the uneven brick bottom of the calcining furnace, coke granules used as fill material also drop between the anode blocks. The baked-on coke granules on the outside of the anode blocks can be removed by a cleaning machine in a subsequent operation; however, the fill material also enters through the anode-rod openings at the front end of the anode blocks. Consequently, after the calcination process the hollow spaces of the anode openings are not only conglutinated with coke granules but also burned because the atmosphere is not entirely free of oxygen. Moreover, a deformation of the anode openings occurs especially in the lower rows of anode blocks because of the pressure exerted by the higher-placed anode blocks. Consequently, all anodes must be cleaned after the calcination process, whereby the plugs previously inserted to seal the anode openings are chiseled out by pneumatic hammers. Because of the previously discussed conglutination, burning, and the incidence of deformation of the anode holes, the rate of depletion is almost 30-percent, so that an excess of anode blocks must be produced to maintain the continuous operation of an electrolytic cell; for instance, the cryolite electrolytic cell for producing aluminum. In larger aluminum plants the daily production of anode blocks amounts to about 2,000 pieces, so that--assuming an average loss of 27 percent and the cost of producing one anode block to be about DM 1,000.00--the daily loss exceeds half a million German marks.
Using those circumstances as the point of departure, the invention addresses the problem of improving a plug of the type described above in such a way that the plug, despite simpler and cheaper production and easier handling, allows the anode openings to be filled in a basically more form-fitting manner, thereby excluding deposits of coke granules; displacing the oxygen in the hollow spaces to a large extent; and effectively preventing the deformation of anode openings.
To solve the problem, the invention basically proposes that the plug be designed as a die-formed part and consist of material containing cellulose.
The plug of the invention provides a form-fitting seal of the anode openings, so that coke granules used to fill the gaps cannot reach the recesses of the anode blocks. Consequently, conglutination of the anode openings with fill material no longer occurs. Moreover, the extreme form-fitting precision with which the plugs of the invention can be produced out of pressed, cellulose-containing material makes it possible to displace the oxygen in the gaps of the anode openings to a large extent and, consequently, to prevent the occurrence of undesired burns during calcination. These plugs of the invention, made of pressed, cellulose-containing material, exhibit a high degree of solidity, so that deformations of the openings are also avoided for the anode blocks positioned in lower rows within the calcining furnace. Another decisive advantage of the plug of the invention is the fact that at the end of the calcination process, that is after the anode openings are already precipitation-hardened, the cellulose-containing material is carbonized. The charcoal, coal dust or ashes remaining in the anode openings at the end of the calcination process, can easily be vacuumed in a subsequent operation. Thus, with the plug of the invention a smooth operation can be achieved in the production of anodes and, consequently, in the total electrolytic extraction of metal. Aside from easy production, the material used also accounts for the low production cost of the plug.
An initial, special design application of the invention, provides that the plug contain wood shavings, wood fiber or similar wood products.
For another application of the invention the plug may also contain paper, for instance, old or recycled paper.
Depending on geographic location, the invention also allows the plug to be made of shaved or chopped sugar cane residues or to use such material as an additive.
According to the invention the plug may, if appropriate, also contain recycled material as an additive.
From the point of view of production technology, it is particularly advantageous to combine the materials of the plug of the invention with an adhesive substance before pressing, a process which increases the plug's solidity even more.
It is also part of the invention to apply a hydrophobic surface layer of, for instance, clear lacquer to the plug of the invention to increase its shelf life significantly.
According to another concept of the invention the plug is made so that it can be pressed into the applicable recess of the anode block.
According to one application of the invention the external contours of the inserted plug essentially fill the applicable recess completely. For it can happen with special mixtures of the anode material--for instance when using certain types of pitch--that the anode material loses solidity during the calcination treatment, especially if the heating phases are of very long duration, so that deformations could occur in the area of the anode openings, particularly in the lowest rows of anode blocks within the furnace. Another cause of anode-opening deformations is the fact that in case of vibration-induced higher density of the anode material, the anode bulk reaches the higher area of the anode openings less consistently. Extremely high dimensional stability of the anode openings is assured because the plug of the invention essentially fills the applicable recess completely, because said plug has, for instance, at least in part a force fit where its external radial periphery sits in the recess and where the open end of its neck presses against the bottom of said recess.
For easy handling the plug can herein be equipped with a, possibly conical, indentation--extending from the top of the plug in the direction of the plug's neck--for inserting a centering mandrel or a similar centering or loading tool for inserting the plug into the respective anode opening.
The head of the plug is appropriately designed as a collar wherein the external wall surface is basically conically tapered in the direction of the neck. Frequently cylindrical counterbores are incorporated into the anode openings to provide additional support for the subsequent sealing of the anode rods with molten iron. Because of the precise form-fit of the collar in the cylindrical counterbore of the respective anode opening, the plug closes flush with the surface of its collar at one of the external sides of the anode block and thus prevents an accumulation of fill material even in this area. When the plug is inserted into the anode opening the conically-shaped external surface, aside from offering little resistance due to friction, also provides an effective seal.
To facilitate the insertion of the plug even more, its neck, in accordance with the invention, is slightly cone-shaped.
In yet another proposed application of the invention, the neck at it open end exhibits an entrance slant, preferably designed as a bevel, which is particularly advantageous for feeding the plug of the invention automatically into the anode block.
In another design of the invention, the plug, at the open end of its neck and extending in the direction of its top, exhibits a basically centric recess and an indentation, which extends from the upper side of the top in the direction of the neck and is peripherally placed in line with the recess, for stacking plugs one above the other. To provide for easy storage, the plugs of the invention can be stacked in vertical and horizontal rows in a storage container or on pallets to save space and to have them picked up from the warehouse together with the container or on pallets, for transport to a loading facility. Because of the way the plugs are positioned within a stack, a loading tool in one operation can grip several of the plugs, which are arranged in stacks one next to the other, and insert them simultaneously into the anode openings of the anode blocks, which may, for instance, have been consolidated into one bundle. The plugs will generally be produced in the areas where the raw materials needed for their production--that is the cellulose--containing material--are available in sufficient quantities or where they appear as byproducts; this will usually be away from the metal-producing plants. However, because the plugs of the invention are stackable, transportation costs are relatively low. For instance, an internationally standardized container for road, rail, water and air transportation can accommodate about 28,000 of the plugs of the invention, which corresponds to a 15-day supply in one of the larger aluminum plants.
To improve the stability of the plugs when stacked, the invention provides that the indentation, at least in parts, has a contour that corresponds to that of the neck, at least in the area of its open end.
Here it is particularly advantageous when a stacking shoulder is formed within the indentation of the plug.
In another application of the invention, the stackability of the plugs can be optimized if the indentation in the direction of the stacking shoulder tapers conically at an angle of inclination which basically corresponds to that of the neck's bevel at said indentation's radially external periphery.
From the point of view of production technology, it is also particularly advantageous if the indentation is designed to accommodate the centering sheath, or a similar centering or loading tool, for inserting the plug into the respective anode opening.
In accordance with the invention, the neck can be provided with an external thread to assure a particularly firm hold of the plug within the anode opening when needed.
Additional goals, advantages, characteristics and application possibilities of the current invention are apparent from the following description of design applications which is based on the drawings. All herein described and/or figuratively portrayed characteristics are the subject of the current invention either individually or in any desired appropriate combination, irregardless of the way they are combined or referred to in the claims.